As a result of a continuous increase in the integration degree and reliability of an integrated circuit, an analog circuit and a digital circuit are integrated and developed in one chip. Also, an analog circuit and a system play an important role in realization and application of a high-density Integrated Circuit (IC) technology. For example, nearly all high-density IC systems employ an amplifier, a filter, a detector, a comparator, etc.
FIG. 1 illustrates an analog filter structure where analog variable amplifiers are configured in two stages according to the related art.
Referring to FIG. 1, an analog variable amplifier 100 of a first stage includes an operational amplifier and two variable resistors R1 and R2. Depending on the implementation, the analog variable amplifier 100 of the first stage may include one variable resistor and one variable capacitor instead of the operational amplifier and the two variable resistors R1 and R2.
Likewise, an analog variable amplifier 102 of a second stage includes an operational amplifier and two variable resistors R3 and R4. Depending on the implementation, the analog variable amplifier 102 of the second stage may include one variable resistor and one variable capacitor instead of the operational amplifier and the two variable resistors R3 and R4.
In each analog variable amplifier stage, a gain is determined by a ratio of the input resistors R1 and R3 to the feedback resistors R2 and R4. Assuming a transfer function of the operational amplifier is A(s), the gain is expressed below by Equation (1). In an ideal operational amplifier, a gain has a value of R2/R1 or R4/R3 in its infinity. Also, the gain of the entire circuit is represented as product (G1×G2) of gains at respective stages. Here, G1 is the gain of the analog variable amplifier 100 of the first stage, and G2 is the gain of the analog variable amplifier 102 of the second stage.
                                          G            1                    =                                                    R                2                            ⁢                              A                ⁡                                  (                  s                  )                                                                                    R                1                            +                              R                2                            -                                                R                  1                                ⁢                                  A                  ⁡                                      (                    s                    )                                                                                      ⁢                                  ⁢                              G            2                    =                                                    R                4                            ⁢                              A                ⁡                                  (                  s                  )                                                                                    R                3                            +                              R                4                            -                                                R                  3                                ⁢                                  A                  ⁡                                      (                    s                    )                                                                                                          Equation        ⁢                                  ⁢                  (          1          )                    
Here, the variable gain amplifier is configured by controlling the values of the input resistors R1 and R3 or the feedback resistors R2 and R4. In the analog variable amplifier 100 of the first stage, when R1 is greater than R2, the variable gain amplifier performs attenuation. When R1 is less than R2, the variable gain amplifier performs amplification. Likewise, in the analog variable amplifier 102 of the second stage, when R3 is greater than R4, the variable gain amplifier performs attenuation. When R3 is less than R4, the variable gain amplifier performs amplification.
Meanwhile, in a case of configuring an analog amplifier requiring a range from −40 dB or less to 0 dB or more, an analog filter processes a wide operation range via two or more analog amplifier stages. For example, a first analog amplifier stage processes −20 dB or less to ˜0 dB or more, and a second analog amplifier stage processes −20 dB or less ˜0 dB or more, so that the entire gain becomes −40 dB or less ˜0 dB or more.
However, an analog filter including a plurality of amplifier stages consumes twice more power compared to the case where one amplifier stage amplifies an analog signal, and requires twice more area, so that manufacturing costs increase.
Therefore, there is a need for an analog amplifier including a single amplifier stage.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.